Chromatin and mitosis: longitudinal splitting of the nuclear threads in cell division

1879–1882 Life and health observation

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A description of the division of the cell nucleus as a continuous metamorphosis: a skein of threads, loops, a star, an equatorial plate, and above all that each thread splits lengthwise, so that both daughter cells receive an identical set. The stainable part of the nucleus he named chromatin, and the process itself, mitosis.

The description was given in 1882 by the German Walther Flemming. He took salamander cells, stained the nucleus so that one part of it held the dye and another did not, and compared fixed with living cells. In Olby's account Flemming's merit was to force many scattered descriptions of division into a single framework and to rule out direct division of the nucleus.

The individuality and persistence of the separate threads he did not yet make out; for that, material with few chromosomes was needed.

Why this date

Dated by the book 'Zellsubstanz, Kern und Zelltheilung' (Leipzig: F. C. W. Vogel, 1882), in which Flemming brought together the results of the three papers 'Beiträge zur Kenntnis der Zelle und ihrer Lebenserscheinungen' (Archiv für mikroskopische Anatomie 16, 1879, pp. 302-436; 18, 1880, pp. 151-259; 20, 1882, pp. 1-86). The word 'mitosis' dates from 1879; 'chromatin' was coined in 1880 according to Olby's DSB article, while Lamm, Harman and Veigl place the definition of chromatin in the 1882 book. The date follows the year of the book, the label the whole series.

What it grew from

• Microscope and the discovery of the cell

  prerequisite for · Confidence: medium

  The stages of nuclear division could not be told apart until objectives and staining techniques improved: Olby names the poor resolving power of lenses and inadequate staining as the reason for the failures of the 1850s, and Bechtel and Bollhagen ascribe the success in characterizing nuclear events to work with improved microscopes and stains.

  Dispute: None of these authors draws a direct line from the microscope of Hooke and Leeuwenhoek to Flemming: between them lie the achromatic objective of the 1830s, water and oil immersion and Abbe's optics at Zeiss. The link rests on the claim that without improved lenses and staining nuclear division could not be made out, not on a succession of particular instruments.

  Link sources

  • Robert Olby, Flemming, Walther, Complete Dictionary of Scientific Biography (1972) Verified 20 Sep 2026

    In the 1850’s attempts to study the process of cell multiplication were vitiated by inadequate techniques of staining and the poor resolving power of lenses.

  • William Bechtel, Andrew Bollhagen, Philosophy of Cell Biology, The Stanford Encyclopedia of Philosophy (2021) Verified 20 Sep 2026

    This focus on separate machines in the factory was promoted in the late nineteenth and early twentieth century when, using improved microscopes and applying stains to enhance contrast, investigators began to identify structures within cells and theorize about their functional significance. Researchers were particularly successful in characterizing the nuclear events in cell division and fertilization. Flemming (1879, 1882) described in detail how the threads that he called chromatin (due to their absorption of dye), later named chromosomes, divided longitudinally

  • Mitsuhiro Yanagida, The Role of Model Organisms in the History of Mitosis Research, Cold Spring Harbor Perspectives in Biology 6 (9), a015768 (2014) Verified 20 Sep 2026

    In the 19th century, pioneering researchers who developed light microscopic techniques discovered characteristic thread-like structures in dye-stained cells before cell division.

  "Verified" means that on that day the quotation was found at the address given, word for word. No date means we have not been able to open the source yet, not that the quotation is wrong.

What grew out of it

• 'Das Keimplasma': the continuity of the germ plasm and the mouse-tail experiment

  influenced · Confidence: medium

  Weismann built his germ plasm theory with the cytology of nuclear division before him: the longitudinal splitting of the threads shown by Flemming gave him the image of equal and unequal division of the hereditary substance, from which he inferred the reduction division.

  Dispute: Robinson notes that Weismann was influenced most strongly not by Flemming himself but by Wilhelm Roux's interpretation of mitosis, and that Weismann used the 'threads' as ready cytological material for a speculative scheme. The link is therefore drawn as influence and not as a prerequisite.

  Link sources

  • Gloria Robinson, Weismann, August Friedrich Leopold, Complete Dictionary of Scientific Biography (1976) Verified 20 Sep 2026

    Since he did not subscribe to the structure Naegeli claimed for the idioplasm, Weismann continued to develop his own concept, but kept in mind the cytological researches then under way.

  • Gloria Robinson, Weismann, August Friedrich Leopold, Complete Dictionary of Scientific Biography (1976) Verified 20 Sep 2026

    In 1875 Oscar Hertwig had seen the appartent fusion of the nuclei during fertilization; and in 1879 Walther Flemming had clearly shown that the threads seen in the nucleus split longitudinally, and had pointed to the possible significance of this segmentation.

  • Frederick B. Churchill, Weismann, August Friedrich Leopold, New Dictionary of Scientific Biography (2008) Verified 20 Sep 2026

    When Weismann introduced the term amphimixis in 1891, he was building on two decades of research in nuclear cytology

  • William Bechtel, Andrew Bollhagen, Philosophy of Cell Biology, The Stanford Encyclopedia of Philosophy (2021) Verified 20 Sep 2026

    Soon after researchers such as Weismann and Correns pointed to links between chromosome transmission and heredity, but it was Boveri (1902) and Sutton (1903) who provided the compelling evidence that Mendel’s factors (what would soon be called genes) are in or on chromosomes.

  "Verified" means that on that day the quotation was found at the address given, word for word. No date means we have not been able to open the source yet, not that the quotation is wrong.

• Boveri's multipolar mitoses: chromosomes are qualitatively different and individual

  influenced · Confidence: medium

  The longitudinal splitting of the threads described by Flemming became the fact to be explained: Roux proposed that each chromosome carries its own set of hereditary elements and that the splitting divides them equally, and Boveri set out to test the qualitative difference of chromosomes.

  Dispute: The author of the Biology article dates the confirmation of Roux's scheme to 1904, that is, to Boveri's theoretical work rather than to the 1902 experiment from which the date here is taken. Olby moreover stresses that Flemming precisely did not see the individuality and persistence of the separate threads, so Boveri started from his observations but arrived at a conclusion of opposite import, that chromosomes are not alike.

  Link sources

  • Ehud Lamm, Oren Harman, Sophie Juliane Veigl, Before Watson and Crick in 1953 Came Friedrich Miescher in 1869, Genetics 215 (2), 291-296 (2020) Verified 20 Sep 2026

    Following Flemming’s own aforementioned coining of the terms chromatin (Flemming 1882) and “mitosis” (Flemming 1879), in the late 1880s Theodor Boveri began to suggest that individual chromosomes in fact carry different parts of the hereditary complement, with each chromosome representing a unique repository of the previous generation’s traits (Boveri 1888, 1892).

  • Richard Robinson, History of Biology: Cell Theory and Cell Structure, Biology (Macmillan Science Library), encyclopedia.com (2002) Verified 20 Sep 2026

    Wilhelm Roux (1850–1924) proposed that each chromosome carried a different set of hereditable elements and suggested that the longitudinal splitting observed by Flemming ensured the equal division of these elements. This scheme was confirmed in 1904 by Theodor Boveri (1862–1915).

  • William Bechtel, Andrew Bollhagen, Philosophy of Cell Biology, The Stanford Encyclopedia of Philosophy (2021) Verified 20 Sep 2026

    Flemming (1879, 1882) described in detail how the threads that he called chromatin (due to their absorption of dye), later named chromosomes, divided longitudinally, with the two halves moving apart so that one of each would end up in each daughter cell (Figure 3). Soon after researchers such as Weismann and Correns pointed to links between chromosome transmission and heredity, but it was Boveri (1902) and Sutton (1903) who provided the compelling evidence that Mendel’s factors (what would soon be called genes) are in or on chromosomes.

  "Verified" means that on that day the quotation was found at the address given, word for word. No date means we have not been able to open the source yet, not that the quotation is wrong.

• 'The Chromosomes in Heredity': chromosome behaviour as the physical basis of Mendel's laws

  influenced · Confidence: medium

  The picture of division in which the nuclear threads split and separate into the daughter cells is the cytological language in which Sutton described the behaviour of chromosomes and set it beside the segregation of Mendelian factors.

  Dispute: Sutton's nearest sources on the cytology of division are Montgomery and Wilson rather than Flemming himself: Martins shows that Sutton took his interpretation of synapsis from Montgomery and that his understanding of the reduction division was still Weismannian. Flemming is the general ground here, not a direct teacher, hence the medium confidence.

  Link sources

  • William Bechtel, Andrew Bollhagen, Philosophy of Cell Biology, The Stanford Encyclopedia of Philosophy (2021) Verified 20 Sep 2026

    Flemming (1879, 1882) described in detail how the threads that he called chromatin (due to their absorption of dye), later named chromosomes, divided longitudinally, with the two halves moving apart so that one of each would end up in each daughter cell (Figure 3). Soon after researchers such as Weismann and Correns pointed to links between chromosome transmission and heredity, but it was Boveri (1902) and Sutton (1903) who provided the compelling evidence that Mendel’s factors (what would soon be called genes) are in or on chromosomes.

  • Lilian Al-Chueyr Pereira Martins, Did Sutton and Boveri propose the so-called Sutton-Boveri chromosome hypothesis?, Genetics and Molecular Biology 22 (2), 261-272 (1999) Verified 20 Sep 2026

    Sutton and other researchers of that time were strongly influenced both by cytological knowledge grounded in observations and theoretical presuppositions that led to interpretations with no observational basis.

  "Verified" means that on that day the quotation was found at the address given, word for word. No date means we have not been able to open the source yet, not that the quotation is wrong.

Links under review

• Mauveine: the first synthetic aniline dye from coal tar

  influenced · Confidence: low

  The last link, from Perkin's mauveine to the cytologists' dyes, was built by the editor: the sources confirm the synthetic dye industry and the staining of chromosomes with aniline dyes separately; no historian of dyes joining them is cited (to look for: Bracegirdle, A History of Microtechnique; Clark and Kasten, History of Staining).

  Chromatin is named after the dye: Flemming saw it and named it because the nuclear threads bound an aniline dye, that is, a substance of the very coal-tar industry that grew out of Perkin's mauveine.

  Dispute: The weak point of the link is that neither Yanagida, nor Lamm and co-authors, nor Bechtel and Bollhagen trace Flemming's aniline dyes back to Perkin's industry: they say only that the dye was an aniline one. The industrial origin of such dyes is supported by a separate source that says nothing about Flemming, so the last step is supplied by us. Besides, carmine and haematoxylin, also used by cytologists, are not aniline dyes, and part of Flemming's work was not done with them; hence the low confidence. The core already carries a link of the same construction, mauveine to Koch 1883.

  Link sources

  • Mitsuhiro Yanagida, The Role of Model Organisms in the History of Mitosis Research, Cold Spring Harbor Perspectives in Biology 6 (9), a015768 (2014) Verified 20 Sep 2026

    For visualization of chromosomes, Flemming used aniline dyes, which bind to chromosomes.

  • Ehud Lamm, Oren Harman, Sophie Juliane Veigl, Before Watson and Crick in 1953 Came Friedrich Miescher in 1869, Genetics 215 (2), 291-296 (2020) Verified 20 Sep 2026

    By staining cells with aniline, the German cytologist Walther Flemming consequently identified a structure in the nucleus that absorbed basophilic dyes a full decade after Miescher’s discovery, coining it chromatin in 1882 (Flemming 1882).

  • William Bechtel, Andrew Bollhagen, Philosophy of Cell Biology, The Stanford Encyclopedia of Philosophy (2021) Verified 20 Sep 2026

    As noted in Section 2, Flemming named the nuclear structures he observed chromatin since they bound the aniline dye he was using.

  • Robert Olby, Flemming, Walther, Complete Dictionary of Scientific Biography (1972) Verified 20 Sep 2026

    he improved Flesch’s fixative in 1882 by addition of acetic acid to give Flemming’s fluid; he introduced Flemming’s stain (safranine-gentian violet–Orange G) in 1891.

  • Edelstein S. «Perkin, William Henry», Complete Dictionary of Scientific Biography (via Encyclopedia.com) (2008) Verified 20 Sep 2026

    Perkin’s discovery gave impetus to a new coal-tar dyestuffs industry.

  "Verified" means that on that day the quotation was found at the address given, word for word. No date means we have not been able to open the source yet, not that the quotation is wrong.

Node sources

• Robert Olby, Flemming, Walther, Complete Dictionary of Scientific Biography (1972) Verified 20 Sep 2026

  Here he carried out the major part of his great work on cell division published in his classic book, Zellsubstanz, Kern und Zelltheilung (Leipzig, 1882).

• Mitsuhiro Yanagida, The Role of Model Organisms in the History of Mitosis Research, Cold Spring Harbor Perspectives in Biology 6 (9), a015768 (2014) Verified 20 Sep 2026

  Flemming described the behavior of chromosomes during mitosis with amazing accuracy in an 1882 collection entitled, “Cell substance, nucleus and cell division.” For visualization of chromosomes, Flemming used aniline dyes, which bind to chromosomes.

• Robert Olby, Flemming, Walther, Complete Dictionary of Scientific Biography (1972) Verified 20 Sep 2026

  In 1880 he coined the term “chromatin” for the stainable substance of the nucleus; the nonstaining portions he termed “achromatin.”

• Robert Olby, Flemming, Walther, Complete Dictionary of Scientific Biography (1972) Verified 20 Sep 2026

  Flemming’s contribution was to force the data from a wide range of apparently differing division processes into a single framework, to rule out so-called direct division of nuclei by simple fission, and to perceive longitudinal division of chromatin loops as the basis of nuclear multiplication, rather than transverse division as Strasburger believed.

• Robert Olby, Flemming, Walther, Complete Dictionary of Scientific Biography (1972) Verified 20 Sep 2026

  Although he noted the same number of loops in successive divisions he did not perceive their continuity and individuality. This called for material with much lower chromosome numbers than he used.

• Ehud Lamm, Oren Harman, Sophie Juliane Veigl, Before Watson and Crick in 1953 Came Friedrich Miescher in 1869, Genetics 215 (2), 291-296 (2020) Verified 20 Sep 2026

  Coining and defining chromatin in his groundbreaking 1882 book, Zellsubstanz, Kern und Zelltheilung, Walther Flemming wrote “[p]ossibly chromatin is identical with nuclein, but if not, it follows from Zacharias’ work that one carries the other.”

• Neidhard Paweletz, Walther Flemming: pioneer of mitosis research, Nature Reviews Molecular Cell Biology 2, 72-75 (2001) Verified 20 Sep 2026

  Flemming, W. Zellsubstanz, Kern und Zelltheilung (F. C. W. Vogel, Leipzig, 1882).

• Ehud Lamm, Oren Harman, Sophie Juliane Veigl, Before Watson and Crick in 1953 Came Friedrich Miescher in 1869, Genetics 215 (2), 291-296 (2020) Verified 20 Sep 2026

  Following Flemming’s own aforementioned coining of the terms chromatin (Flemming 1882) and “mitosis” (Flemming 1879), in the late 1880s Theodor Boveri began to suggest that individual chromosomes in fact carry different parts of the hereditary complement

"Verified" means that on that day the quotation was found at the address given, word for word. No date means we have not been able to open the source yet, not that the quotation is wrong.

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